Investigation On The Positional Selectivity For Enzymatic Synthesis Of Structured Lipids

Fats and oils are the major source of fatty acids, and play an important role in the human three major nutrients, TAGs are condensed by one glycerol molecule and three fatty acid molecules, which are accounted for more than 95% of the edible oils. The nutritional value and physicochemical properties of TAGs depend not only on the fatty acid composition, length of the carbochain and fatty acid unsaturation, but also on the positional distribution of acyl groups bonded to glycerol, which have an important effect on the bioavailability of fatty acids. Even if the composition of fatty acids in edible oils are similar to each other, but the different acylation of fatty acids can make various oils physical properties different, which further led to the big difference of the absorption of fats in the body metabolism and determined the fats nutrition and application values.The “positional effect of fatty acids acylation” of TAGs is important to guide the research of functional oils and fats products. Structured lipids(SLs), as a new kind of functional lipids, which have been studied extensively in deep processing of oil field by using chemically catalyzed reactions, enzymatically catalyzed reactions to modify the fatty acid composition and positional distribution in the glycerol backbone. Enzyme-catalyzed synthesis of SLs has advantages over chemical synthesis in terms of practical applications such as those involving high catalytic activity, more specificity, less by-products, mild reaction conditions, environmentally friendly processes and can obtain the unreachable products. However, the specificity of lipase can be achieved in appropriate conditions, different reaction conditions, acyl donors, reaction medium and different physical auxiliary processing conditions have a significant impact on the location specificity of lipase. Research on the enzymatic catalytic reactions including the fatty acids acyl migration and position specificity and selectivity is a basic research work and worthy of attention in lipid chemistry, this study can also provide theoretical support for the modification of function lipids. Hence, the major results of this study are as follows:1. Combined with the solid phase extraction and gas chromatographic detection, the analyzation method of fatty acids distribution on α and β position and composition of glycerides of SLs was established, TAG, DAG, MAG and FFA can be separated in turn on a small solid phase extraction column, the method was successfully applied to the analysis the practical samples;2. The present work has studied lipase-catalyzed synthesis of OPO type SLs. This approach effectively enriched the OPO content via ultrasound pretreatment in organic media using microtip probe. Optimal reaction conditions for the pretreatment were 50% ultrasonic power, 6 min pretreatment time, 3 s/9 s of ultrasonic pulse, PPP/OA molar ratio of 1:8, 12% dosage of Lipozyme RM IM and reaction temperature of 50 °C. Reuse of Lipozyme RM IM for 10 cycles under ultrasonic irradiation did not cause essential damage to its lipase activity. The apparent kinetic constant of ultrasound pretreatment reaction was 2.52 times higher than the conventional mechanical stirring;3. In this paper, ethyl ester form of LC-PUFAs purification method by urea complexation was established; enzymatic interesterification was carried out with the purified ARA ethyl ester(ARA-EE) and tripalmitin(PPP). Response surface methodology(RSM) was used as a statistical tool to model and optimize the reaction parameters with a three-level, four-factor Box-Behken design. Moreover, acyl migration of different fatty acids to the sn-2 position was also examined. This obtained symmetrical ABA-type SL contain both palmitic acid at the sn-2 position and ARA at sn-1, 3 position and is possible used in the food and nutraceutical industry.